In a conventional power production facility a high number of wind turbines may transfer electric energy into an utility grid. Commercial and/or private consumers may consume energy taken from the utility grid. Thereby, the energy demand or power demand of the consumers may vary with time.
In particular, during large changes in the energy demand of the consumers, the energy demand or power demand of the consumers may not match the energy transferred from the power producers (in particular one or more wind turbines) to the utility grid. In this situation, in a conventional wind turbine, the power output or energy output of the wind turbine, in particular the power output of a converter of the wind turbine, may be increased for a short period of time, in order to improve the balance the amount of energy transferred from the wind turbine to the utility grid and the energy demand of the consumers taken from the utility grid. In particular, the frequency of the grid may drop, when the energy demand of the consumers is greater than the energy transferred from the power producers (in particular one or more wind turbines) to the utility grid. In contrast, the frequency of the utility grid may increase, if the energy transferred from the power producers (in particular one or more wind turbines) to the utility grid is greater than the energy consumed by the consumers.
When the output of the converter of the wind turbine is increased for a short period of time to recover the frequency of the utility grid (such as 50 Hz for Europe or 60 Hz for the United States) more kinetic energy is pulled from the rotor of the wind turbine resulting in a slowdown of the rotational speed of the rotor. Thereby, an efficiency of the wind turbine may be reduced. Thus, the increase of the output of the converter of the wind turbine may be followed by a recovery time, where a lower production can be exported.
US 2007/0120369 discloses a system and a method for utility and wind turbine control, wherein the wind turbine system includes a controller comprising an internal reference frame of the wind turbine generator coupled to the converter and configured for modulating flow of power through the converter in response to frequency disturbances or power swings of the utility system relative to the internal reference frame. In order to boost the output temporarily during a low frequency event, the converter of the wind turbine would have to be overloaded temporarily. This may not only increase the load of the converter but may also increase the load on the turbine drive train. Thereby, disadvantages may be encountered.
There may be a need for a method and for a system for controlling an electric device of a wind turbine, wherein a stability of the utility grid may be maintained or at least improved. In particular, there may be a need for a method and a system for controlling an electric device of a wind turbine, which do not require to overload a converter of the wind turbine during a power swing, thus avoiding corresponding disadvantages.